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Diffusionless transformation
A phase transformation occurring extremely rapidly via collective atomic shifts without long-range chemical diffusion. The most common example is the quenching of austenite to form martensite.
Diffusionless transformation is an abrupt process where the structure flips over without atoms moving. When welding, this happens if you cool the weld too fast – then hard, brittle martensite forms, which cracks. This is especially a problem with higher-strength steels. You have to slow down the cooling, for example by preheating or letting it cool slowly, so the structure can transform cleanly and the weld stays tough.
MetallurgieSchweißtechnik